Connectors for supplying direct current (DC) power are poorly standardised compared to domestic alternating current (AC) power plugs and sockets. A DC plug is a commonly used term for one type of cylindrical two-conductor plug available in a range of sizes and usually used to power small pieces of electronic equipment. The most common use of the DC plugs is on the cable connected to a power supply. The matching jack or socket is then mounted in the equipment to be powered. Several competing standards exist for DC plugs. In some cases, incompatible plugs can be fitted into sockets, possibly damaging equipment and leading to a poor current supply.
Cylindrical DC plugs generally have an insulated tip constructed to accept insertion of a pin into a bore within the plug. The outer body of the plug is one electrical contact, most often but not always the negative side of the supply. A pin mounted in the socket makes contact with the second internal contact when inserted into the bore of the plug. The outer plug contact is often called the sleeve and the inner the centre contact, although the tip itself it usually non-conductive. At least two different national standards exist, EIAG in Japan and DIN in Germany. As well as these standards, several conventions have been adopted by specific manufacturers to indicate voltage by plug size.
Contact ratings vary from less than 1 Amp up to 5 Amps with a 2 Amp current being typical. The voltage which can be supplied again varies and is usually under 100 Volts, with a 12 Volt power supply being typical.
The most common type of plug found in the art will have an approximate outside diameter (OD) of 5.5 mm and a length of 9.5 mm. However, two pin sizes are commonly used in the jacks for this size of plug body, 2.1 mm and 2.5 mm. For best electrical contact, the bore within the plug should match the diameter of the pin. However, the two sizes are very similar and can easily be confused even when seen together. The sizes are also not usually marked on either the plug or the socket.
One of the disadvantages of the conventional pin connector is the possibility of electric arcing between the pin and the bore of the inserted plug which surrounds the pin in a mating connection. The contact between the centre pin and the inserted plug relies on interference between the plug and the bore which surrounds it when the plug is inserted into the socket. In many cases, due to normal manufacturing tolerances, the dimensions between the mating parts of a socket and a plug are not precise and a bad connection is obtained as a result.
As noted above, it is difficult to distinguish a 2.5 mm DC plug from a 2.1 mm DC plug even when the plugs are seen together. The bore of a 2.1 mm DC plug is too small to fit a socket having a 2.5 mm pin. By contrast, a bore of 2.5 mm in a DC plug will fit a 2.1 mm pin, but may not make enough contact to work effectively and the contact interference between the pin and the bore may not be made sufficiently. In extreme cases, this will result in electric arcing which may product sufficient heat to induce burning. In other cases, no contact is made at all and no power supply is provided.
Various solutions have been proposed, including the provision of a locking DC connector which uses a threaded fitting to secure the connection between the plug and socket. However, such threaded systems are difficult to use with a wired DC plug. There is accordingly a need to solve the problems discussed above and to ensure that there is always a positive contact between the socket pin and the bore of the plug.
The present Applicants have now realised that by improving a socket connector to be more flexible to dimensional variations, all of the above-mentioned disadvantages can be overcome.